From Adam's interview with Esquire:
Have you started working on the next season of Workaholics yet?
No, we start up in about a month. We're excited to keep it moving and shaking. I'm leaving on Monday to go shoot a movie called Mike and Dave Need Wedding Dates. I play Mike and Zac Efron plays Dave. We shoot in Hawaii until August. I'm really excited. It's going to be the best.
When you stand next to Zac Efron and you see his body, how do you feel?
Horrible. I am literally going to an appointment right now with a nutritionist. I hired Chris Pratt's personal trainer and his nutritionist to get in shape. I've lost 15 pounds. I went from 18 percent body fat to nine percent in a month and a half. I'm doing it!
jeezbee was nice enough to write up an explanation about the characters because we were thinking Zac would play Mike and so Adam's answer was like... wut? Anyway here is what Bee wrote:
As you may notice, Adam says that Zac will play Dave and not Mike as we've been assuming. I was 100% sure that the trades had reported Zac will play Mike so I went back to check. It turns out that Variety must have quietly changed this part of the article later on and we all missed that. (In case you're in doubt... here is the old version of the article we were all going off from on a syndicated source).
What does that mean? Well, it looks like Zac will be playing Dave after all (as I had assumed initially). Since Anna Kendrick will play Zac's wedding date, it means she will play Alice not Tatiana because that is Mike's wedding date. Which leads to Aubrey Plaza playing Tatiana opposite Adam DeVine's Mike. Of course unless the trades and Adam got it wrong but this constellation makes sense.