Although Canada and Ukraine have not interacted in Hetalia, many fans pair them on the basis of history. There is a large population of Ukrainians who migrated to Canada, and many still do. Fans believe this is a contributing factor as to why Ukraine and Canada would have a positive relationship, among other things. Canada's fighting support of Ukraine's independence is also often used to support their close relationship.
Fans believe their similar personalities may have brought them together as well, and often portray Ukraine as one of the (few) nations to actually notice Canada and distinguish him from America. Both characters are seen as 'down-trodden', Canada because he is never noticed/acknowledge/recognized and is constantly mistaken for America, and Ukraine because of her relationship and situation with Russia. Both characters also seem to be very shy and under the "shadow" of two superpower countries, Canada to America and Ukraine to Russia.