There are many possibilities and scenarios that could happen in the second leg, you can see in the picture below, Arsenal is the favorite with only @1,24 odds. But we know that Porto have an advantage on the aggregate side which makes them more confident in playing defensively.
Well, with all of these and as I said before, I wouldn't bet on this match because the risk is too high.
I can't believing with sport bookie how come giving large odds for FC Porto who won the first leg match, actually difficult acceptable and interested for put betting to bet Porto looking for the match result on first leg not close the potential win back to back on away and home match. I think FC Porto have advantage with aggregate 1-0 and they not in under pressure position for facing Arsenal in second leg. Don't losses bigger opportunity with unbelievable odds and I think FC Porto has chance for defeating Arsenal in their home match.
Well, with all of these and as I said before, I wouldn't bet on this match because the risk is too high.
Have two weeks later for second leg match between Arsenal vs FC Porto, Arsenal return to winning performed in domestic league after defeating Newcastle United last match but I don't think easily for defeating Porto on second leg match.