im building a 33 gal acrylic aquarium. 3/8 cell cast acrylic. I'm not quite sure how hard it is to get weld on # 4 in canada. Im looking at getting it quickly so i can start this build. What else could work besides weld on?

When building a tank you really want to use the correct supplies.

You can use chloroform but it involves major protection

These guys ship to Canadia

http://www.ridoutplastics.com/adandcem.html

Do a google search IPS weld-on Canada

http://www.google.com/#hl=en&safe=off&...d121c88310e67e3

the place where im getting my acrylic cut has some metyhlene chloride. (i believe that's the full name) i'll definitely be doing my acrylic work in a well ventilated room.

Methylene chloride will work....

You know, it'd be a lot easier to help you if you took the time to put your location in your user details.

There's a plastics shop in northeast scarborough that carries weld-on, but unfortunately I have no idea if that's anywhere near you.

Remember to rough cut about 1/8" oversize then rout down to your dimension. You want a "baby's bottom smooth" edge before 'gluing".
Use some kind of "spacer" to space the two pieces apart for the solvent to melt the area of bonding. Those ty wraps in the grocery store will work, just strip the paper off one end and space every 6" apart.
Also the table you will be using usually is not flat across, use some kind of wedge to bring the bottom up and the wire spacer will be snug. Not tight but snug. This will be the correct spacing for the solvent to wick into and remember in about 20 secs take them out, let the top piece fall into the sofftend area to bond.

PVC cleaner is a good sub. ive build tanks with it and never leaked. its been over a year + since i built it