Most venting occurs at the chest and neck. A good garment will allow you to tighten up all the openings if the weather really turns sour. So look for a jacket with a hood that allows some movement, and opens easily if conditions are changing rapidly. For hard paddling a breathable top is nice except if it starts to rain or the weather picks up. This will allow water to bead and maintain breathability.
Saltwater wreaks havoc with most breathables.
This is because the salt crystals dry on the outside and some make their way inside. The salt entices the water into the jacket increasing the dampness inside. Mesh liners in waterproof jackets add some softness but will increase the drying time and risk of dampness. Mesh liners are often preferred because they feel nicer next to the skin rather than the coating on the jacket. Waterproof breathable fabrics are better around camp than on the water.