Yes. A Canon flash can generally be mounted on a Nikon hot shoe, and a Nikon flash on a Canon, and the flash will usually fire in sync with the exposure.

What typically works:

• basic hot-shoe triggering
• manual flash use, if you set power on the flash itself

What typically does not work across brands:

• TTL/i-TTL/e-TTL metering
• high-speed sync/FP
• camera-menu control of flash settings
• flash exposure compensation from the camera
• wake/sleep communication
• lens-linked zoom control
• other advanced brand-specific features such as some wireless or rear-curtain options

Why: the center sync contact is standardized on most ISO hot shoes, so the camera can send the basic “fire now” signal. But the extra contacts and communication protocols used for advanced features are brand-specific.

One caveat: Sony historically used a different hot-shoe design on older cameras, so physical compatibility was different there.

So for simple on-camera manual flash, cross-brand use is usually fine; for TTL and advanced automation, it generally isn’t.