You do not need UV filter because the Canon L lens already got UV inside the lens. All you need is the best clear protector filter like B+W clear MRC protector filters to protect your expensive lens.Where did you get that piece of information?
The sensor in a current dSLR is effectively insensitive to UV light (I've empirically tested this with a 7D and 5DII, an appropriate light source with UV/Vis emission, and a set of narrow bandpass filters). Therefore, for a dSLR there is no difference between using a clear filter and a UV filter. My advice is to get whichever is cheaper and/or more readily available for you.