What test should my doctor request to determine my active B12? Can I get that test done in Ontario, Canada?

No, there’s no test your doctor can run to determine your cellular B12 activity. I need to look at the results of your Organic Acids Test, and that test cannot be done within Ontario. You can’t get it through your doctor or a local lab. You need to order it online from Great Plains. 

Some people go to their doctor and ask for the "Active B12" test. There’s this test called “Active B12”. But it’s actually quite useless and doesn't tell me anything at all. It sounds like a nice test in theory. But it doesn't actually measure Active B12 like they say it goes. It doesn’t tell me whether you are B12 deficient or not.

The test has a stupid name. It simply measures the amount of B12 that is bound to transcobalamin II. Transcobalamin II is the B12 carrier responsible for B12 uptake into the cell. But the test does not determine if you have the active forms of B12. It only measures whether you have sufficient B12 to saturate your circulating transcobalamin. But the B12 can be any form of B12 (active or inactive). Therefore, the test is not useful and badly named. I wouldn't recommend it.

So no, there is no test you can request. I need to see your Organic Acids Test results.  

I do like to see Serum B12, because it's somewhat helpful to see. But you can have normal Serum B12 and still be deficient. So the Organic Acids Test is the most helpful.