Canon 1D 4.15 MP Vs Nikon D3000 10.2 MP?

I know it also has to do with sensor size
Added (1). And I shoot ONLY IN manual

Apples to oranges. The D3000 is a VERY entry level camera, crop sensor
The 1D is a professional camera, full frame sensor
If the megapixels are giving you a hang up, check out the MegaPixel myth (google is your friend)
If you don't already know how to use the DSLR in manual mode-where you set all of the settings-don't buy the 1d. There's no auto mode and your pictures won't work until you learn a whole bunch about the exposure triangle

Umm… Are you aware that you are comparing apples and oranges?
The 1D (mark 1) used to be a high end professional grade camera, in 2001.
The D3000 is a lower entry level camera from 2009.
The D3000 will outperform the 1D in terms of sensor performance my virtue of being 8 years newer.

You have a lot to learn. Before you spend a dime, consider taking a basic class in photography.
The Nikon full frame camera is the D3 (The Canon 1D is a full frame camera. Almost (APS-H.
The D3000 has been upgraded to a D3100. The corresponding Canon would be the 1100D/T3