...(by extension from "loonie" although they missed a trick not calling it a "doubloon")...

Who's they? It's not called a 'toonie' in any official context, and when it first came out, there were all kinds of people wanting to call it a 'doubloon(ie)'. But 'toonie' (sometimes spelled 'twoonie', though not as much these days) won out.

Hell, 'penny', 'nickel', 'dime', and 'quarter' aren't official names either. I imagine they're loans from American English.