In a few months I have a PIT-FRA (via YYZ) trip coming up and I will be checking 1-3 valuable knives. The knives will be appropriately wrapped and packaged. What can I do to ensure that they do not "disappear" en route to my final destination?

If they're quite valuable I'd ship them insured via common carrier like Fedex or UPS to your destination. As seen by oodles of posts here there is no foolproof way to avoid unscrupulous airline or government employees.

The only other approach which comes to mind is the unloaded flare gun trick where you put said 'weapon' in your bag & declare it to the airlines as a firearm. Makes it illegal for others to open the case outside of your presence but might add a ton of hassle to your trip. Search the forum for more detail (and make sure said item isn't illegal at your final destination or in-transit stops).

1. Flare gun a bad idea. Take a look at Canadian law. I have no idea what German law is, but would want to check that as well.

2. Use the Fedex/UPS route w. insurance.

3. Valuable items are excluded from coverage under the COC for almost every carrier, so you are SOL if you put them in checked luggage.

That seems like the right answer.^

I have flown with my knife roll inside my checked in luggage 8-10 times a year for the past 30+ years without a problem.
I use a non TSA lock on a Wusthoff branded professional knife roll. The luggage bag has been checked by TSA on occasion, but never had the lock cut off the knife roll. I used to declare them to the check-in agent as professional tools; but I haven�t even done that in the past few years. I can honestly say that I have never heard first hand from another Chef of knives being taken from checked luggage. On the other hand, I watch them like a hawk when in a strange kitchen or public event.
Interestingly, my golf clubs/bag always gets the TSA lock cut off and thrown away; and has been missing sleeves of balls more than once.

Thanks for the feedback folks. Looks like I will be sending them via FedEx.