A friend suggested why be adventurous and give my 16GB (from my 40D) a try in the G3, after I take everything off it and reformat it on my computer ... so I did.
I reformatted the card on my computer as FAT32 with 32K clusters. Put the 16BG CF card into the G3 and ... WOW ... it sees it. Great!
So at least we now know a Kingston ElitePro 16GB CF card works in the Canon G3.