Hi Tee,
The great tent debate - many options available. Depending on how big your kids are (e.g. under 6?), what you plan to store in your tent (any packs?) you may be able to get away with a 3 man tent for the 4 of you. I was looking at this tent (Mutha Hubba by MSR) at Bushtukah, and Mt Coop carries it as well: -
http://www.mec.ca/Products/product_detail.jsp?PRODUCT%3C%3Eprd_id=845524442618564&FOLDER%3C%3Efolder_id=2534374302702837&bmUID=1213818590470.
Lots of tents on sale at Bushtukah at the moment, including some very nice 3 and 4 man Big Agnes 3 season models.
I like the ventilation and weight of the Mutha Hubba, and it packs extremmely small. Best advice is to go in, set the tents up that meet your requirements and lie down in each with your 'possy' (wife/kids if possible). Can you live with a low roof height? Can you live with a norrowing at the feet? Can you live with ultralight construction (sacrifice in strength and durability)?
In the end I didn't purchase the Mutha Hubba. It looks like a great tent with ample room but it turns out me and the kids can sleep in my 3 season 2 man NFace tent (10 years old) for the 8 nite trip along Tim River. It's a tight fit, but we can all lie somewhat comfortably - the last year I can get away with it. Next year I'll be buying something bigger (such as the Mutha Hubba or equivalent 3 seasoner). I have a 20 year old 4 man MEC 4 season tent (too heavy and not ventilated enough for this Summer trip), 3 year old 6 man Sierra Bedouin (WAY too big for this trip) and a couple of NFace Goretex Bivy sacks and 1 hammock.
Good luck.