I think, that of all the lunar new year animals, the rat is possibly the least likely to appear on a stamp at any other time. For both of the Year of the Rat stamps (2008 and 2020) Canada has chosen to go with the 'mouse bride' or 'rat's wedding' story*.
This left one from 2008 is so colourful and fun. I love the purple, the parasol, the purse, and the little curl in the bride rat's tail. On the right is this year's version, with the bride rat being carried in her chair, or litter. Personally, I prefer the 2008 version.
*You can read an interesting version of the rat's wedding here
for Sunday Stamps - lunar new year animals
Gong Hei Fat Choy (one of many variations in spelling of Mandarin)