I have a valid US B-1 visa, so just wanted to check if I can transit via Seattle.
And if my connection flight is only 1.30 hours, will I be still able to make it?
If you are flying from Canada into Seattle then almost surely you will clear the border at the Canadian airport as almost every Canadian airport (Vancouver YVR, Calgary YYC, Toronto YYZ -- Victoria YYJ being the only exception) that has a direct flight to SEA has a US pre-clearance facility.
B1 visa is plenty to enter the USA, yes.
If you cleared the border then 90 minutes is more than enough. Otherwise, you need at least two hours (according to SABRE).