score:2
Looks like it'll be option 1 unless you can get a good roaming deal at home before leaving. I travel a lot between the two countries and also only really care about data, as far as I know there's no prepaid-SIM that even allows roaming between the two. For a long time I was using dual SIMs RedPocket / Koodo, it seem though the best option is getting a US contract from T-Mobile that includes data and text roaming in most countries, including Canada, but this is only open to people with US residency.
In the US, among others Net10 and StraightTalk SIMs are widely available in shops locally. T-Mobile also has some good value plans in their stores ($45/2GB). I prefer RedPocket's service and rates, but SIM cards are hard to find locally outside of Chinatowns.
Canada is unfortunately rather expensive, I think Kodoo is the best option if you're looking for data though their coverage is limited to urban areas, the SIM is around $20, a base plan to get your line activated for a month is $15 you can add data $30/GB.
Upvote:1
Not a complete answer, but I used Similicious during a month long trip to Canada from the UK last year. Can't fault them. I took data only (used skype for calls, but they have voice/data plans), they asked about where I'd be to ensure best provider (was primarily in Alberta so got Rogers and 4G for most of the trip) and device to ensure correct sim type was sent and phone was capable.
SIM was dispatched to me in the UK without problems, they asked dates I would be there, and it just worked when I put the phone on in Calgary airport (in fact I ended up streaming Spotify for the last few days as I had too much data left!)
So I'd endorse them wholeheartedly for Canada.