I signed up for the UA Business card in May last year and received the SUB last year. My GE expires in mid July and the business card does not offer a reimbursement. I think at the time I had planned to sign up for the CSR aftewards but I don't feel it is worth it since I currently have the Venture X. (I gave away the GE reimbursement from that card to my mom less than 4yrs ago).

If I sign up for the UA Explorer card now or in May after I've cancelled the Business card, am I eligible for the SUB? (The last time I got one from the personal card was more than two years ago)

If I understand correctly, The answer is yes. I asked chase and they gave an confusing answer based on quotes from terms vs just answering directly so I want to make sure.