A recent Apex Legends datamine has suggested that Titans might be coming to the game, although it might not be in the way you hope.
Apex Legends dataminer Biast12 recently uploaded a video on their Twitter, showcasing the abilities of the as-of-yet unannounced Legend Blisk. The video is two minutes long and shows Blisk calling in a Titan, which slams into the ground and acts as a turret for a couple of seconds before exploding.
In the video, the Titan is referred to as an "Auto-Titan", which further suggests that it's only available as a wide-spread turret attack, and not as an AI companion of sorts. Being able to climb into a Titan would provide a pretty unfair advantage after all, as well as likely not being possible in the Nintendo Switch port of Apex.
It's previously been confirmed that Apex Legends and Titanfall are in the same universe, so it does make some sense that Titans can appear in this universe. Considering Apex Legends is a battle royale with a lot of players, it also makes sense that they can only act as a brief special move and not be controllable at all.
If the name Blisk sounds familiar to you Titanfall fans out there, he's actually appeared in both of the Titanfall games and played a pretty significant role. He's also already a part of the Apex Legends lore, although he's much older than he was in the Titanfall games. With both of these factors in mind, it makes total sense that if Blisk was in Apex Legends, he'd try and use a Titan to help him out.
Blisk is just one of the many leaked Legends coming to Apex. Dataminer That1MiningGuy posted a design document listing several characters that have since come to the game, and a few that are still unreleased like Valk and Blisk himself.
Of these characters, Blisk is listed as a "future character", implying that his release is still pretty unknown. This datamine would suggest that most of his moves are in place and that he has entered full development, meaning that he might not be far off.