What are the parallels between the characters of to a mouse and Of Mice and Men?

I think what is even more telling than the likenesses are the dissimilarities between LENNIE and a mouse. LENNIE - big, bulky, ignorant, and bumbling - is the opposite of a mouse, that we imagine as coniving, premeditating, tiny, quick on its feet, et cetera.
I think that Steinbeck was playing with irony when he chose this particular title.

The title was mainly influenced from a poem by Robert Burns. The line reads "The best laid schemes of mice and men often go awry". Steinbeck alludes to this line to show how Lennie and George's dream will never be accomplished and this is representative of many of the ranch workers at the time who shared a common dream of owning land etc.

Although Lennie is physically opposite to a mouse, his personality is similar: meek-mannered and mild. Also, Lennie carries a dead mouse at the beginning of the novel to 'pet' because he likes soft things.