I'm a Canadian that moved to the US for work - this multiple sounds entirely plausible, in fact it sounds like a conservative estimate.
In major tech hubs the multiple is closer to 3-4x.
> "Much more realistic is a 30% bump"
This is not at all realistic - I know many Canadians working in the US as developers and all of them are making well in excess of 200% of their Canadian market rate.
You're characterizing Canadian tech salaries (in say, Vancouver or Toronto) as being moderately below US standards (~30%?), where in fact they are vastly below the standard in comparable markets (SFBA, Seattle, NYC, etc). The gap is already big for new grads, but it widens even further with experience. A dev with ~5+ years of experience can reasonably triple their salary moving south.