Well, since you are most concerned about fanatical muslims.  The fanatical muslims we read about in Canada are all native-born and mostly white.  So there are definitely converts, but the main problem with your argument is that you cannot extrapolate percentages the way you are doing.  Our sources of immigrants keep changing every few decades, and it would be highly unusual if they stop changing.  The next change is likely to be a decrease in immigrants from China when their population bulge reaches retirement as our boomers are doing now, and skilled immigrants from India with increase.  Then India's population will start contracting, and we may get more immigrants from subsaharan Africa, but we may also be getting immigrants from a failed moon colony by then.  :)