Why did the 1968 Canadian 10 cents have a Philadelphia mint mark?

https://en.numista.com/catalogue/pieces39248.html The other cent piece of that year was an Ottawa mint mark. Did they mint it there because they needed another minter?

Yes. The Canadian Mint couldn't keep up with demand that year, so the Philadelphia Mint was approached and accepted the job. None of those coins have mintmarks.

I cannot speak for the cent, but the mint can be determined on the dime by the style of reeding.

Here is a link to our 68 dime history;
https://www.coincommunity.com/canadian_ten_cents/1968_elizabeth_ii_ten_cent.asp

I can find no evidence that Philadelphia helped Canada mint a recalled material [silver]. Anyone?

The dime struck in Philadelphia was not precious metal.

That's not what this coin page says: https://en.numista.com/catalogue/pieces39248.html

There seems to be a lot of uncertainty about this. My 1968 dimes are all Ottawa, even the nickel ones; I had had several swaps trying to get a Philly dime but the reeding pattern matches other Canadian dimes rather than a US one.

I am skeptical that there was a silver Philadelphia-minted dime. What do the Canadian catalogs say for 1968?

Krause 2016 only includes KM# 72 (Ottawa silver), 72a (Ottawa nickel), and 73 (Philadelphia nickel). No 73a is listed.

I am pretty sure that Numista is wrong on this. The Canadian government paid the US government about 2 cents a dime to be struck at Philadelphia. That would not have been the case if it was silver. I think if someone had a Charlton catalog, that this could be cleared up.

My Charlton Catalogue is a bit vaguely worded, but it implies that no silver coins were minted for Canada in the US.

That's what I thought.

KM 73 is the only 1968 dime that Krause identifies as struck at the Philadelphia Mint--all of them are nickel.