Hi timboab
The 'C' means they are Canadian reg'd a/c which are operated by Sunwing Canada and flown by their pilots. In all other respects they are identical to the rest of the XL fleet. In fact they were G-XLAE/F/H before they were transferred to the Canadian register.
MAN-SFB and GLA-SFB will be operated by XL A330 from 1st May.
Cheers