The 10-time Olympian — a world record — was recognized at the start of the 2012 Spruce Meadows 'Masters' Tournament.
Painted by artist Gordon Milne, the collection began in 2002. It features 15 of Canada's greatest sports icons, ranging from swimmers to boxers, and now includes Millar.
BMO Financial Group, one of Millar's longtime sponsors, donated $10,000 to the Canadian Therapeutic Riding Association in his name.
Millar has been an outspoken supporter of therapeutic riding for those with mental and physical disabilities.
"I've seen the good riding can do for a person," said Millar in a statement. "Riding can heal, and everyone should have the chance to get on a horse."