Directions:

from OTTAWA: Highway 417 -> Highway 7 / Highway 15 to Carleton Place, Smith Falls, Portland (whole drive takes about 1 1/4 hours)

from MONTREAL:
Highway 401 West until Brockville (Exit 696) onto Highway 29 until Forthton, Forthton Highway 42 to Crosby, Crosby Highway 15 to Portland (whole drive takes about 2.5 hours)

from TORONTO:
Highway 401 East to Kingston, Kingston (Exit 623) onto Highway 15 up to Portland (takes about 3.5 to 4 hours)