It's certainly legal to marry her - who you marry is entirely your choice. However she will have to sponsor you if you want to come to Canada and live here - and there is no guarantee the sponsorship application will be approved. To be approved, you will have to show that your marriage is genuine. Since you have such a large age gap, you can expect that CIC will examine your file extremely closely to make sure the marriage is genuine and you will have to provide a lot of supporting evidence to prove that you do in fact have a real relationship and aren't just marrying her so that you can move to Canada. If you have never met - make sure you don't marry on the first trip where you meet her in person. This will significantly increase the chances that CIC will think your relationship is not genuine and you are just using her to get to Canada.