Random searches in October (ITA Software, from: dub::bd ac+, to: sfo::ac+ bd):
Fare (A1): AC DUBYMQ K0MSLXL fare (rules) €176.50
Fare (B1): AC YMQSFO L5QSTP fare (rules) C$240.50
Fare (B2): AC SFOYMQ L5QSTP fare (rules) C$240.50
Fare (A2): AC YMQDUB K0MSLXL fare (rules) €176.50
... plus the usual junk, total cost US$1140, within your price range.
Note that as these are two fares combined (at Montreal) you can stopover there in either or both directions at no cost.