Most likely, I think, if two young women went to Canada, one maybe 17/18, one in her early 20s, they would have gone under some sort of domestic program in which immigration agents found them work in Canada and brought them over specifically to fill positions (housemaid, nanny, that kind of thing). Alternatively, the elder one had met her husband in England at some point and followed him to Canada, taking her sister with her.
Emigration was always seen as the chance for a better life; perhaps they also had, if not relatives (cousins?), friends from their town who had gone over and sent back letters about how well they were doing. Perhaps a friend of theirs had married a Canadian soldier during WWI and ended up in Toronto, for example.
Sometimes people are just listed in the emigration records by surname and initial (E. Smith) or just "Miss Smith", so you may have to play a bit with the records to find them. If you do find possibles for them leaving from the UK, you can try to pick them up in the records coming into Canada which might show more information.
If you give their names I'm sure people will be happy to try and help you find them.
