Coming to Vancouver you have 3 options.
Best: YVR - Vancouver. Fly straight in. Rapid transit to the port (downtown), or a variety of car services. Using rapid transit you can be downtown less than 20min after getting through security/your bags. Cons: Cost is higher from the US, you need to deal with airport customs.
SEA - Seattle. Another large airport approx 3hrs drive south and a border from Vancouver. Often much cheaper, but you will need to get to Vancouver. There are 2-3 coach bus lines that do the trip (Quick Connect, FlixBus), which will take about 4-5 hours. Another option is taking the train (Amtrak), which is also reasonable on price, but you need to take the rapid transit line from the airport to the international district of Seattle to catch the train. Train also only leaves 2x day (one in the morning, one in the evening)
BLI - Bellingham. Small airport in a town 1h south of Vancouver (and a border). Southwest flies here. Downside is QuickCoach is about the only coach bus to stop here, and it is hit and miss. Other coach buses (eg: FlixBus) stop in Bellingham, but not at the airport. Amtrak also stops in Bellingham, but the station is about 20m south of the airport via car/taxi/uber.
If you want the least stress, fly direct to Vancouver. The cheapest is likely bellingham or seattle, but remember the added costs for the coach buses / trains and getting to the stations.