Canspace.ca gives you new registrations at $10.99 and the same for renewals, which is rare.
WHC.ca gives you new registrations for $9.99 which is probably their cost but the renewals are $13.99 which are $3 higher than Canspace.
Also WHC has a ton of specials to register at cheap rates so they probably need the $13.99 to subsidize the specials.
I have had hundreds of domains at WHC and Hundreds at Canspace and always had to transfer between the two to take advantage of pricing. I finally moved most to GoDaddy with the Domain Discount Club that gets me $11.99 for both .ca and .com.
So for me the short answer is...
Canspace for renewals - best price ongoing
WHC for registrations - best price ongoing
I think if WHC could give domainers with hundreds of domains a renewal break they would probably end up the clear winner.