A South or SouthEast Wind blowing at 10-15 knots and a small to moderate chop of 2 to 3 feet is a "regular" day in Stephen's Passage. Usually, the water in Tracy Arm itself is completely flat, but there's an hour to 1.5 (where the whales are usually seen) that puts you in Stephens Passage.
Adventure Bound, Alaskan Marine Adventures and Allen Marine all have relatively large boats that handle the "regular" conditions quite smoothly, while other smaller boats either wait for the few totally calm days, or slow WAY down if it's bumpy.
If you know you're prone to sea sickness, there are many things you can do for it, but all must be done BEFORE you go on the water... some a few minutes before, and some days or weeks before...
Better not for now... signatures get me banned!