What that indicates is that Canada's tax rate, for this taxpayer, is about twice what the U.S. tax rate is.  That's not really the case, but a lot of things that are paid by Canada from income taxes is paid by the U.S. with FICA taxes, against which no credit is allowed.   It's like an Illinois taxpayer with California income -- Illinois will only allow a credit in an amount equal to its (lower rate) tax on it.  

There may be rare cases where that carryover can be used, but I don't think I have seen one.