score:3
Yes, some countries do have country-level filters, but they're usually quite obvious with error messages (for example, here's Singapore's), and they tend to target things like p**n and political dissent, not frequent flyer mileage sites.
Incapsula appears to be content delivery network, so the most likely explanation is that Aeroplan uses them worldwide and they had some glitch specific to Croatia. The only potential workaround is to use a VPN, so you appears to be connecting from somewhere else and may be able to connect.