What to Wear on a Cruise and Expectations

I have traveled a lot via plane but this is my first time going on a cruise, so I have no idea what clothes to pack or any expectations of what happens on a cruise while you're not exploring the various stops.

For starters, Im a Caribbean lady who's traveling to Ontario for a week-long cruise, so since obviously my wardrobe is mostly for hot weather, should I invest in thicker/longer material clothing? Also what in general should I pack while walking around the ship? I already have my exploration clothes covered.

Additionally, I'm a seafood lover and would love to try sushi on the ship, but based on other's experiences online it's best to shy away from seafood in general while on cruise ships because they stay out too long and food poisoning is highly possible. Is this true? Is there anything seafood related that might be safe on ships to eat?