best flights routes Singapore to Toronto

There are no any direct flights from Singapore to Toronto, but there are flights from Singapore to Toronto with Transit
Singapore Airlines Flight from SG to YYZ
1) Singapore London Heathrow - Toronto
2) Singapore Frankfurt - Toronto
3) Singapore Milan Malpensa - Frankfurt - Toronto
4) Singapore Dubai - London Heathrow - Toronto
5) Singapore Munich F.J. Strauss - Frankfurt - Toronto

Both Singapore Airlines and Cathay Pacific are Five Star Airlines
Cathay Pacific ~
1) Singapore Changi - Hong Kong - Toronto

All other Airlines need a transfer to other airline.
- JAL
- Malaysian
- ANA
- Asiana
- China Southern
- Thai

the best way is to fly Singapore Airlines to New York, and from New York take any flight, preferably Air Canada to Toronto
You may take any of the above airlines to any US States and take another airlines (Example: Air Canada) to Toronto.