So long as the wind was not blowing downstream, I would use the single spey. I would also try to fish from further upstream(initially) to get the fly swimming in front of the fish. If this was not possible then the double spey is as good a cast as any for getting the fly square across the current.
Without knowing the water temperature, time of year, or freshness of the fish it is hard to say what type of fly to use. I fish in Scotland so know only about Atlantic Salmon in general and certainly know nothing about the fish that run Canadian rivers.
However, here goes, if I was fishing from further upstream and fishing the fly slowly across the fish I would fish a small fly size 10 or 12, assuming a water temperature of around 13-18 C (56-65 F). Pattern would probably be a Stoat's Tail variant tied with a flat silver rib, bright yellow tail, and longer arctic fox wing, or a similar dark fly with a trigger point.
If I was fishing with a squarer cast and the fly was coming across the fish quicker, I would switch to a brighter or flashier fly, and maybe go a size up.
Failing that, I would try a collie dog and then a riffled fly. Also, if I could get to the other bank I would try to pester them with a fly on the dangle.
Then if no fish takes I would leave them in peace and try further down stream for a taking fish. Actually, I would probably have left them in peace after the first two attempts and then come back to them if I could find no more takers.