Hi Kevin, pretty plant you got. That's a pretty ambitious project for somebody in Canada to grow a lemon tree!
First thing I'll say is I would pot it up into at least a 3gal. pot right away. Be very careful with the surface roots (top of the soil) because they are pretty fine and easily torn. Lemons have a lot of feeder roots near the soil surface generally, so disturb them as little as possible. Use a good quality potting soil that is high in peat, and if you can, augment with some sterilized compost. I also add a handful of alfalfa pellets (horse food) to everything I pot up. It's a great soil amendment and seems to give newly potted plants a nice boost.
Second thing, (and we were just advising someone in Idaho the same thing) being as far north as you are, that lemon is not going to get enough daylight, let alone enough sun when your winter days get down to only about 6 hours of light. (I'm originally from Vancouver, BC right "up there" with you). Look into setting up a supplemental light system on a timer for your lemon (and other tropical plants will love it too). Just one grow light bulb isn't going to cut it for a tree. You will need a 4ft. fluorescent ballast set up with T6 daylight bulbs. A minimum of 10 hours total of good light per day will keep the leaves on your tree and keep them green. So if it's getting 4 hours of bright sunlight in the middle of the day in December, set up the lights to come on for 3 extra hours in the morning and 3 hours in the afternoon. Say 8am to 11am, and 3pm to 7pm.
Third thing, buy some fertilizer that is formulated specifically for citrus, because they have "special needs" as far as micronutrients go. It will very likely be in pelleted timed-release form and in a pot, I would use half of what the recommended amount is from March through the summer months (because your soil surface is not as great as if the plant was in the ground) and even less than that through the winter, depending upon how cool your house gets at night. Even with the supplemental light, the plant will slow down growing in the winter.
It should be years before you will need to prune that little tree. But (you're going to hate this) when it blooms the first time, go ahead and enjoy the lovely fragrant flowers but DO NOT let it set fruit its first year. Yes, when the little 'buttons' form after the blossoms drop, pinch them off. This will direct the plant's energy into growing roots and healthy new top growth for a year before it has to make a great big lemon for you. It's a huge sacrifice the first year but you'll be glad you did it in future.
