YOW is a really small airport so lineups at PreClearance will be minimal. Any checked bags will be delivered to the PreClearance area within 15-minutes of arriving, so 45-minutes would not be all that tight at this airport which handles mainly RJs on transborder flights. Walking between areas should not take more than 5-minutes either. The major issue would be a late arrival, but you'd be protected on a later flight, which would be the alternative you can confirm now given the sked change.