Answer: I would go to the library and look through lots of gardening books! Start noting the plants you like the looks of, then check to see if they are hardy in your region. (You may be able to find a regional gardening book, to save you that step.) You might also look for some back issues of gardening magazines (and even subscribe to one--like National Gardening!)
Take a good look at your house and current landscape, and make a "bird's-eye" drawing of it, noting where the ground slopes, where water, power, and sewage lines are, etc. Draw in existing vegetation, and even where the shadows fall during different parts of the day. Then begin to think about whether you want evergreen trees or deciduous trees. (Think about the comfort of your house--deciduous trees will shade the house in summer, but drop their leaves to let sunlight in in the winter.) I like to begin by thinking about "islands" of foliage--perhaps a medium-sized ornamental tree, with some appropriate companion shrubs. Then some flowering perennials to add color and interest.
You will have a challenge creating those French/Mexican visions in your zone 3 gardens. If I were you, I would opt for native plants, and others that are well adapted to that cold. I think that's one of the biggest mistakes a new gardener can make--choosing plants without considering their hardiness and adaptability to the region.
Finally, think small. Don't get too overwhelmed, thinking you have to do it all at once. Start with a small section, see how that works, and add more and more over the years. That's one of the joys of gardening--watching a landscape grow and change over the years.
I came across this web site recently; it might be of interest to you: http://www.ambrosegardens.com/index.cfml
Good luck, and try to enjoy your new adventure! And if you get stuck, you can always call in a professional designer for some tips.
Q&A Library Searching Tips