The Canada Revenue Agency's website, which includes the Charities Directorate, will apparently be moving to the new http://www.canada.ca domain on July 11, 2017. The old CRA pages will remain up during the interim period of the move. Hopefully those visitors who go to pages on the old website will be automatically redirected to the new website.
I have written about this change and my concerns in a blog entitled "Government of Canada to combine all Federal government websites into Canada.ca".
The CRA page will be https://www.canada.ca/en/services/taxes.html
The Charities Directorate page will be https://www.canada.ca/en/services/taxes/charities.html
Ultimately if the www.cra-arc.gc.ca/charitiesandgiving link/website is not available presumably CRA will provide its suggestions as to which link should be used for receipting purposes. As you know the regulations to the ITA state that every official donation receipt must have "the name and Internet website of the Canada Revenue Agency."
Do you require legal advice with respect to Canadian or Ontario non-profits or charities?
Mark Blumberg is a partner at the law firm of Blumberg Segal LLP in Toronto and works almost exclusively in the areas of non-profit and charity law.