Hell, using Bolivar Trask as the head of Weapon X in the second movie would've made more sense than Stryker.
A version of Trask appeared in X3, but he didn't appear to have anything to do with Sentinels in that film. However, he also appeared in the X-Men Origins: Wolverine
video game, where it was shown that he took part in the project to create the Sentinels. Also, the commentary of X3 states that there is a secret Sentinel project going on behind the scenes during the timeframe of the film.