Both Nikon and Canon entry level DSLR have approx same price tag, Nikon D3100 have better Movie mode but limited to Nikon DX and AF-S mount lenses and Canon 1100D support EF & EF-S lenses ,Nikon D3100 have better movie mode and a bit bigger sensor with high resolution.
Conclusion: Nikon D3100 is a overall better camera, Nikon D3100 gives you better movie mode and still shot with 11 AF points, At Canon 1100D Auto-Focus is not available during video shooting, so if you want to shoot images and capture Full-HD Video with you first entry level DSLR, Buy Nikon D3100, If you want to shoot only images with your first entry level DSLR, you should buy Canon 1100D.
See Recommended Lenses
Recommended Lenses for Nikon D3100
Recommended Lenses for Canon 1100D