When saving for the web, Photoshop lets you set some default Output Settings for the filename. Some of these options include the documents name, today's date, and the various slice names. I would like to get some other dynamic info added automatically when saving. Like the total dimensions(WxH) of the canvas,or the color mode (RGB/CMYK). Is there any way to get this info to show up?
You can use File > File Info in order to add metadata to an image. Then, when using Save For Web, change the "Metadata" drop down on the right and choose "All". By default the dimensions and color space (EXIF data) should be included in metadata when choosing All.
The canvas, on images which are saved via save for web, is always the same size as the image dimensions. There is never a Save For Web image which has a larger canvas than the image itself.
This will increase file sizes (kb), sometimes considerably.
I don't know what you mean by "get this info to show up."