The Boise connection in Ontario
Ontario is part of the Treasure Valley, the lowland that runs from Vale in Oregon to Boise in Idaho.
The valley
Wikipedia defines the Treasure Valley as a valley mainly in southwestern Idaho where the Payette, Boise, Weiser, Malheur and Owyhee rivers drain into the Snake River. It lists Ontario among the valley's Oregon cities and calls the Boise metropolitan area Idaho's most populated area.
Distance
Wikipedia says Ontario is about 56 miles (90 km) northwest of Boise by Interstate 84. We do not give drive times, which depend on traffic, weather and the time zone change at the state line.
The state line
Crossing the Snake River means crossing into Idaho. Ontario, as noted on the events page, observes Mountain Time. Payette County, Idaho is part of the Ontario micropolitan area, according to Wikipedia.