First off what type of rabbits are you hunting? common cotton tail or the snow shoe hare?

Either way they leave tracks in the snow and if not disturbed a lot they have regular packed down trails. You can slowly walk those trails and watch for that shiny black eye of the snow shoe hiding near a brush pile trying to blend in with the snow around it but that black shiny eye gives it away.

Cotton tails also will be in thick stuff (bushes). Best day to hunt either is sunny days. As with the snow shoe move really slow and watch for that brown blob in the snow. many times they will almost let you walk on them.

And yes they will be in that marsh if it has grass, at this time of year the water is frozen and the grass will hold snow making a cavity under it for the rabbits to hole up in during a storm.

Al