Thanks for your answer.
I did eventually find a way in the canon driver to split the picture on several pages using the mosaic / poster setup (third tab where you can choose bordless).
For instance using a 2x2 pages I could obtain my picture on page 1 and 2. Unfortunatly, the driver offers very little control on the overlapping margins.
I will probably end in cutting the picture in half in photoshop, unless I found a nice program to do this.