What are your color settings in Photoshop (especially color management policies)? Which color profile does ACR assign to imported photos?
If I understood correctly, you did this:
1) Opened the RAW in ACR and modified it
2) Saved it *from ACR* to a file
3) Opened that file in PS
In this case which color profile is used depends on what profile ACR assigned to the image, and the color management settings of Photoshop, especially what happens if Photoshop working profile and the image embedded profile don't match.
If you open the CR2 directly from Photoshop, it still goes through ACR, just it pass the data directly to Photoshop (without any lossy JPEG compression, if a JPEG file is used). Even if your final format is JPEG/sRGB, is far better to get RAWs in Photoshop in a larger space (ProPhoto, AdobeRGB) and 16bit, which will allow for more editing without degrading the image much, and then convert to sRGB and output to JPEG as the last step (maybe to a copy so the image can still be better edited if needed).