Hello tessie_gardener,

North American carnivorous plants would be just the ticket. Two in particular would be just about perfect for zone 4-5 weather if they are protected from totally freezing into a block of ice in pots. The Northern Purple Pitcher Plant, Sarracenia purpurea purpurea, grows in the Northern area of the United States and into Canada. In addition, the Round Leaf Sundew (Drosera rotundifolia) is a very hardy sundew that grows in zone 4 weather right next to the Purple Pitcher. If you created a mini-bog in your yard, you could plant them in it and not even worry about protecting them too much in winter so long as they are insulated by plenty of moss, water, and other plants growing around them.

Technically, quite a few of the sarracenia will survive in Canada if you make sure to mulch over them durring the cold months so they don't freeze. I will say, the purpurea is your best bet due to the fact that it grows so far north already, but I've heard tell of several different sarr being grown by hobbiests in Canada.

Here is a link that might be useful: Aracknight's Deadly Delights

Are you considering only those that can be placed outside? If you have sunny window sills, you can grow many sundews, butterworts, and bladderworts that do well and flower, withouttaking up much space and have low maintenance.