A lot of the 'tax' you're seeing is the YQ or "fuel surcharge" that AC collects supposedly on behalf of the partners who request it. So what you want to do is avoid those carriers.

As of a redemption i did about a year ago or so, the carriers to avoid were: AC, LO, LH, NH, OS, OZ, TP (i still ticketed on OZ due to their high quality product if not top-notch piloting skills).

That may seem like a lot, but not really, as it still leaves you a fair amount of choice and (some) decent product out there. Since that time, as far as i can recall, the only major carrier to have joined the alliance is BR, so no idea if AC levies YQ on them.

As for actual 'taxes', you want to avoid LON (and to a lesser extent CDG) as an origin, destination, or stopover point if on a premium-cabin ticket (revenue or award) due to the heavy 'Air Passenger Duty' tax.


edited to add: link to the only 'official' list on YQ that i can find:

https://www3.aeroplan.com/whats_new/...670_2011_11_10