Most important is selecting cold hardy varieties that are suitable for US hardiness zone 4, which shouldn't be difficult for apples or pears, but peaches can be finicky, and you should be choosy with the peach variety. I myself would look into the 'contender' variety for a peach tree, the 'fuji' apple variety should do ok in your area, but 'honeycrisp' for example, is more suited. And for pear try to look into the 'golden spice' variety, but 'bartlett' or 'bosc' should be ok  as well. Ultimately any labeled for zone 4 hardiness should be OK. You are technically 4b (-20 to -25)

Secondly, know that you may need a second apple, or a second pear if you haven't already, as these trees will need a cross pollinator of a different variety, or may not produce a fruit. The peach tree, though, can self-pollinate, so you can get away with only one of those, but a late frost can and often does ruin a peach harvest. That's another reason the 'contender' peach is great because not only is it very cold hardy, but it's also a late bloomer. 

Lastly choose varieties that are not only hardy, but disease resistant. Apple scab can be terrible for apples, and firelight for pears. Peach, too, unfortunately can also get a plethora of problems, but nothing as common year after year as apple scab or fireblight. And be aware of varieties that are manageable for your space - commonly these trees are grown on different root stocks that allow the tree to be a more manageable height, dwarf (8'-10'), or semi-dwarf(12'-15'), or standard (18'+), so you're able to plan accordingly.

Best of luck!