The field on this coat of arms is green, to represent a green field like those found in Ireland (where many of the original immigrants were from) and also to represent Champlain, the French explorer who first passed through the area (champs = field). The sword represents the veterans of the Napoleonic wars (who were given land in the area) and of the War of 1812 (where we burned the white house to the ground!!). The wavey lines represent the Otanabee River.

The red lion as a supporter is taken from the Duke of Wellington's coat of arms, as many of the Napoleonic veterans served under Wellington.

This was actually the second official coat of arms granted to a city in Canada, and there is an official version here.