Originally Posted by
Blumie
I think people are being too conservative. If the OP's flight is reasonably close to being on time, 2:40 leaves plenty of time for a LGA-JFK transfer by taxi, even with luggage. Forget the shuttle bus or any other option; take a taxi, which will cost about $30 with tip and take 20 (unlikely) to 45 (likely) minutes.
Nine times out of ten the AC flights into LGA are delayed by about 20 minutes leaving Canada, then a few circle patterns so flights are usually 30 minutes late arriving. Baggage can take time too but my experience has been within fifteen minutes, so that leaves the taxi ride and the ck in deadline to deal with. There is not much time to spare at all but it is feasible.