Fans are already abuzz in speculating just how the upcoming Baldur's Gate 3 will tie in with the original games. Developer Larian Studios has already confirmed that there will be connections, likely multiple ones since the history of Baldur's Gate is so rich, but it's still a mystery what those connections will look like.
One thing known for sure is that certain characters from the original Baldur's Gate saga will appear in Baldur's Gate 3, and given the sheer number of optional companions present in BG, BG2, and BG2: ToB, that leaves a number of possibilities. Roughly a century will have passed between the events of the original saga and Baldur's Gate 3 so that naturally rules out (most of) the human characters, but some of those other Dungeons & Dragons races are plenty long-lived enough to still be kicking--and available for a cameo.
Viconia DeVir
Viconia DeVir, as one of the drow elves, has the capacity to live well over 700 years, which would certainly mean she'd be alive in late 15th-century DR when Baldur's Gate 3 takes place. She's a powerful priestess of Shar, having fallen out of favor with the Spider Queen Lolth (the usual patron deity of drow elves) after refusing to sacrifice a baby in her name. Viconia fled to the surface, leaving House DeVir and the Underdark behind her, and can potentially join forces with the player character of the original Baldur's Gate series.
She can also supposedly die if romanced, as the ending slide for a player character in a romance with Viconia states that she is eventually murdered by agents of Lolth. However, it's highly unlikely that'll be kept as "canon" for future Baldur's Gate adventures, seeing as romance in the games was also entirely optional and Viconia wasn't the only romanceable character. Assuming her death isn't canon, she'd certainly be available to guest-star in BG3. After all, the notoriously l0ng lifespan of elves is also the reason that Drizzt Do'Urden has a series of over 20 books with no signs of stopping.
Jaheira
Jaheira, meanwhile, isn't a full-blooded elf, but her status as both half-elf and powerful druid gives her a pretty decent chance to make it into BG3. Jaheira was a member of the Harper faction (though this becomes a turbulent matter in Baldur's Gate 2), and originally came into the company of the Baldur's Gate player character through association with their adoptive father--also a Harper. Headstrong and dedicated the balance of nature, a mass slaughter orchestrated by mind flayers could certainly be enough to draw Jaheira back into the action.
Half-elves generally live between 180 to 200 years, so depending on her age in Baldur's Gate it's possible that she'd still be fit for battle as well. Plus, considering the D&D druidic class's Timeless Body ability that kicks in at level 18, she could very well appear exactly the same as she did in Baldur's Gate 2.
Jan Jansen
Every game needs a touch of comic relief, right? Even the traditionally dark Baldur's Gate series. That's not to say the eccentric turnip salesman isn't also good at his job as a thief and illusionist wizard, but he's definitely got some interesting quirks stemming from his life as an inventor and, yes, turnip farmer.
The gnomish race wasn't terribly popular in previous editions of Dungeons & Dragons, to the point that the 4th edition cut them out entirely, but they've enjoyed a resurgence with 5th edition. Gnomes are typically capable of living to around 350 years, which means Jan could, logically, involve himself in the events of Baldur's Gate 3 in some way. How he'd be involved is another story, considering Jan's hobbies, but the possibility is still there.
Aerie
Though she no longer has her wings, Aerie is a member of the avariel elves; they're a winged subrace of elves that are relatively rare in the world of Faerun. To say she had a rough childhood would be an understatement, as Aerie was sold to a circus and had her wings chopped off due to infection, but she's a powerful cleric/mage companion in Baldur's Gate 2. And though she's quite naive and inexperienced in those games, current-day Aerie might not be if she kept to the adventuring lifestyle. As an elf, she'd once again most definitely be alive in BG3, and goodness knows her abilities would be useful in a pinch--or, say, a mind flayer invasion.
Coran
Coran is actually one of the few party members of Baldur's Gate to be mentioned outside of the games. He makes his first appearance in Baldur's Gate as a potential companion, an elven archer (specifically, a fighter/thief multiclass) with a tendency for womanizing. He's not featured so heavily in the second game, although he can be optionally encountered in the Forest of Tethir along with another former companion, Safana. It's also been established in the Legends of Baldur's Gate comic that Coran lives a steady life in Baldur's Gate by 1479 DR, and since Baldur's Gate 3 takes place only a decade or so later, he may still be there when the mind flayers arrive.
Minsc (and Boo!)
Of all the characters who might make a return in BG3, Minsc and his trusty miniature giant space hamster Boo are the most likely. Minsc is actually human, and normally wouldn't be alive to see BG3, but his status as one of the most iconic Forgotten Realms setting characters to date has been his saving grace. As revealed in Legends of Baldur's Gate, Minsc was petrified into a statue and has only recently become unfrozen (Coran was the one to bring him up to date when he woke!), so he's both alive and in the area.
Minsc and Boo returned to the adventuring life after rejoining the land of the living, so if anyone is going to help BG3 players ensure that butts are liberally kicked in good measure, it'll be this dynamic duo. Where Minsc goes, evil stands aside. And who knows? Maybe fans will finally get to see Boo go for the eyes!
Baldur's Gate 3 is currently in development for PC and Stadia.