I took the ferry last week between Tsawassen and Swartz Bay (Victoria), travel was on a Tuesday and Wednesday. Given I had a five hour drive to get to the ferry and am not familair with wait times, I made a reservation. I arrived at the ferry terminal early, caught an earlier ferry (6pm) that was showing only 37% full 45 mins before departure. For the return I caught a later ferry than my res and again far from full.

Given I don't take the ferry very often, I enjoy it. The weather was spectacular, the scenery is incredible through the Gulf Islands and Active Pass.
One aside, I decided to have dinner on the ferry on the way to Victoria. I think it was a newer ferry with a buffet restaurant called Pacific somethin or other. The food was excellent in comparison to what I expected and good value IMO C$27.