If you're comfortable with using wildcard whitelist entries, then we'd recommend you simply allow HTTP and HTTPS access to *.twinkl.ca / twinkl.ca.
Using this wildcard whitelist entry will ensure access is allowed for all our currently used sub-domains, plus any additional ones we may begin to use as Twinkl continually develops.
You may also want to whitelist HTTP & HTTPS access to one or more of our geographical TLD (top level domains). For example, either *.twinkl.co.uk / twinkl.co.uk, *.twinkl.com / twinkl.com or *.twinkl.com.au / twinkl.com.au.
You should easily be able to tell that you need to take this action if you can't access the Twinkl website and you see a non-.ca/.com website address in the address bar.