Usually I'd be against converting a "failed" starter turned good reliever back into a starter, but Varland's profile isn't the sexiest for a reliever, at least this season. Maybe next season they can work on generating more K's/swing and miss as a reliever, assuming they want to keep him in that role, but if they view him as a SP option long-term then it wouldn't be the worst option to try it out. If he had Brendan Little's profile as a RP where he was striking everyone out with lots of swing/miss then I'd be temped to leave him in the pen, but that hasn't been the case. That's where the 5 years of control is beneficial. They have time to figure it out.
Based on everything i've read about Rojas, I think he would have helped the 2025 bullpen. Him panning out as a SP given his injuries and lack of innings might be a bit of a long shot, but the profile seems there for a high leverage reliever. Of course it wouldn't have been a lock for him to come in and succeed right away, and the Jays wanted to maximize 2025, as they should, so this swap likely made sense for that reason. Will be interesting to see how this trade looks over the years. The Twins have done a good job developing RP's (as witnessed by the trade deadline) so Rojas is probably in a good spot if that's his best role.