This is simply the nature of nearly all SLR cameras. They have to flip the mirror up out of the way in order to take video (or shoot stills using Live View). When the mirror is up, the focus screen is covered and the optical viewfinder is blacked out. Keep in mind that SLRs are primarily a still photography camera, and shooting video is sort of an add-on feature.
You can get shades and loupes for the LCD screen, that might help. Or use a dark cloth, the way we did shooting with large format film view cameras! 
If you use a particular focal length, you also might be able to use an accessory viewfinder that fits into the hot shoe of the camera. This would remain usable even during video or Live View shooting, but will have paralax error issues with close-up objects, and you'll have to be careful to match the angle of coverage of the viewfinder with that of your lens.
Alternatively, there are some SLR cameras with Electronic Viewfinders that stay "live" during video or Live View shooting. Those often have a bit of delayed response, though, which may make it difficult to use with any degree of accuracy with moving subjects.
Or just keep using your Power Shot for videos and use your DSLR for still shots (the DSLR is undoubtedly a much better camera for still shots... if nothing else the considerably larger image sensor will give superior image quality).
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & PRINTROOM
