RONKONKOMA — After plans to get JetBlue to Long Island MacArthur Airport were grounded, officials have set their sights on landing Air Canada. A letter written by The Long Island Association and Purolator Inc., Long Island’s largest freight carrier, was sent to the airline’s president urging them to set up a Long Island-Toronto flight. According to reports, the letter suggested that such a route would lower the airline’s cost due to a less congested airspace. There is no information yet on whether Air Canada has considered the proposal.