If your network consists of the MP450 being shared from a Windows computer, then you will not be able to use the Canon driver. This is because the driver has been written to work on a direct USB connection only, and that is why it doesn't appear in the Canon list of printers.
What you will need to do is look at using a driver that will work across your network and that is the most compatible with the MP450. You have the option of the free drivers from Gutenprint, which you can get from Sourceforge, or buying the PrintFab software. Note that the MP450 is not listed as a supported printer with Gutenprint, so you will have to try a few options to get the best output, whereas it is listed as a supported printer by PrintFab.