I am not on the visa waiver list and am in the US with a valid US visa, and plan to catch a flight from Vancouver to Hong Kong. I plan to enter the border from Seattle on land, and then go directly to YVR. Am I eligible to apply for a transit visa or I have to apply for visitor visa?

The above is scenario A, for another scenario, that I fly from NY to YVR and want to do a stopover in Seattle (enter by land too) and then go back to YVR on land after several days, am I eligible for the transit visa?