Black Oranda, we have a few different sized ponds, all built that same way. One is 250 gl, two are 650 gl, and the big one holds 1200 gl around. They have all been running for years with no problem or leaks. For the biggest one we made a concrete base, just to be on the safe side. The others have plywood as base.
Its addicting, I tell you! Once you see how nice they look , you want more and more!

Or course, if you only have limited space awailable, you might be better off with a rubbermaid container. They come in different sizes as well, from 100 gl up to 300 gl. Or you can check out
Aquatic Ecosystems, thats where I got my 160 gl tubs from. You might find something similar in Canada.

Here is the ones I got
http://www.aquaticeco.com/aquatic1v1/itemp...passitemid=6643