I really don't like this name, any spelling of it. It sounds like a servant's name to me: "Maisie, quick, bring the master's shaving water!" "Maisie, you foolish girl, you've broken the teapot again!" I picture some bucktoothed girl with pigtails and an apron yes-ma'aming and curtseying all day long in between playing step and fetch it.
Jasper and Maisie sounds like characters in a little kids' storybook. Jasper and Maisie and the Witch's Cake or something like that.