You need to determine WHAT tours you are considering, then locate operators. I do not recommend going to tour operators who are booking agents, extremely easy and superior to deal direct. Look over your shore excursion list and post your interests. For listings of port venders request visitor guides.
Especially in Seward, my top tour recommendation is a Kenai Fjords boat tour, only consider those at least 6 hours on the water, you need to get out of the bay. This is a must do if interested in some great varied wildlife opportunities and very close glacier viewing.