Yes, if it is an old flash, it is possible that the trigger voltage is around 200V. However, according to some information from Chuck Westfall (Canon USA official), all bodies since the EOS 20D should withstand this voltages (I don't have the link, but you can search Google and it will pop up in one of the many forums).

To be on the safe side, you can get yourself a safe-sync device that decouples the electrical contact between the flash and the body.

Anyway, if you want to be sure about the voltage, you can test with a multimeter. The problem is that most of them have a too-low input impedance so the reading is false. You need one with 10MOhm at least. I just got a cheap DMM from Walmart that was actually able to correctly measure the 190V on my old Sunpak flash, where 2 other meters failed and read around 6V. I know it should be 190V b/c it was confirmed by an industrial FLUKE meter and later on by Sunpak representative.

The Walmart one is from the Automotive shelf and named INNOVA EQUUS 3300. It specifically mentions 10 MegaOhm in big writings on the package.

This post may help: http://forums.dpreview.com/forums/read.asp?forum=1031&message=26638040.