There are two non-stops operated by UA (UAX) SFO-YYC. UA should be willing to accommodate on one of those. Other possibilities include SFO-FRA-BEG, SFO-IAH-FRA-BEG, SFO-EWR-FRA-BEG, or SFO-ORD-FRA-BEG.
Alternatively, what would your preferred routing cost if booked today? If the same or less, then cancel & refund what you now hold and purchase a new ticket. While most routings do not get cheaper, it happens.