Pay to be different
If RCAF want to re-engineer the refueling system for the Dave A they will have to pay a shed load of money to do it, as would we if the RAF went down that route. The other option would be to fit a boom to CC-150 / Voyager and train up a cadre of boom operators. That too will be very costly!
With little spare money for either option in both Canada and the UK I just don't see it happening.
Better and cheaper to buy Dave C which has the large weapons bay, larger internal fuel load and a probe already.
Just bacause it's the carrier variant does not mean you need a carrier to go with it, as Ausses and Canadians have shown with F-18.