Is it RMB5100?
Is it include tax?
where did you book them?
I asked an agency,he give me the price is RMB5200(Cathay Pacific,HK-Toronto,include tax),and only two luggage for one adult.

I think maybe your plane is belong to Air Korean, If u have a stop-point in America, u must have a visa.

And I never heard Cathay Pacific have airplan via America to Toronto?
maybe u should chick it on Cathay pacific's Web site.

Good Luck!