I follow and like, but don't love the Jays. I follow them in part because I did in 1980's and 1990's until my (mostly) allegiance switched to the Giants. But for me it is more because I really hate the Seahawks and somewhat dislike the Mariners.
I have followed the 49ers pretty closely since the late 1970's and lived in the San Francisco for almost 12 years. I liked the Seahawks of the Chuck Knox era (Dave Krieg / Curt Warner / Kenny Easley / Steve Largent, etc.) but that didn't interfere with my 49ers loyalty because the Hawks were in the AFC (and they were rivals of the hated Raiders). I was ambivalent to the Hawks in the 1990's, but that changed in 2002 when they became NFC West divisional rivals. For a 49ers fan, the media love-fest for the Seahawks is every bit as irritating as the TSN love-fest for the Leafs.
I also follow the SF Giants and have since the mid 1990's. However since neither the Mariners or Blue Jays are in the NL, they don't compete directly, but some of my Seahawk hate just seems to rub off on the Mariners. Rational? Probably not, but whatever.