Originally Posted by eigenvector

Hmm, after making this post I tried switching to a different endpoint of the same VPN service and got through so you're right, it may just be that one of their servers has been flagged and Aeroplan isn't actively trying to block VPN. Still weird though as this is the first time I've ever seen a blockpage like this and I've been doing most of my browsing through various VPN services for ~5 years.