I finally can display the image using LibRaw together with OpenCV. However, I found that it is okay to display .CR2 files of 5D Mark III but .CR2 files of 5D Mark II. It gives a error:
"An unhandled exception of type 'System.ArgumentException' occurred in System.Drawing.dll
Additional information: Parameter is not valid."
Is there any difference between the .CR2 files of 5D Mark II and Mark III?

My code is:

int check = Processor1->dcraw_process();
//process the image into memory buffer
libraw_processed_image_t *image = Processor1->dcraw_make_mem_image(&check);

//create a Mat object by data obtained from LibRaw
cv::Mat cvImage(cv::Size(image->width, image->height), CV_8UC3, image->data, cv::Mat::AUTO_STEP);

cv::cvtColor(cvImage, cvImage, CV_RGB2BGR); //Convert RGB to BGR

IntPtr ptr(cvImage.ptr()); //create a pointer based on the Mat object image

//Error occurs in the following statement, the last line with 'ptr'
Bitmap^ b = gcnew Bitmap(cvImage.cols,
cvImage.rows,
cvImage.step,
PixelFormat::Format24bppRgb,
ptr); //bitmap object of the image