question edited for clarity and toss in some CAPS.
It doesn't take A3 Paper and doesn't have a Tray No. 4.
A4R is just A4 in Landscape Mode, half an A3.
What is A4 and A4R?
The "R" indicates that the paper is set in the landscape orientation. Paper that can be set either in the portrait or landscape orientation. Paper that can only be set in the landscape orientation. 8-1/2" × 11" A4, B5. 12" × 18", 11" × 17", 8-1/2" × 14", 8-1/2" × 13", A3W, A3, B4.
Tray Capacity No-collate Mode Tray A: 250 Sheets (Letter, Statement-R, Executive) 125 Sheets (Legal, Letter-R, 11" x 17")
Tray B: 1,300 Sheets (Letter, Statement-R, Executive) 650 Sheets (Legal, Letter-R, 11" x 17") Tray C: 2,450 Sheets (Letter, Executive) 1,700 Sheets (Statement-R) 650 Sheets (Legal, Letter-R, 11" x 17") Collate and Group Mode Tray B: 1,300 Sheets (Letter, Executive) 650 Sheets (Legal, Letter-R, 11" x 17")
Tray C: 1,700 Sheets (Letter, Executive) 650 Sheets (Legal, Letter-R, 11" x 17")
Staple Mode Tray B/C: 1,300 Sheets/100 Sets (Letter, Executive) 650 Sheets/
https://copiersonsale.com/wp-content/uploads/brochures/Canon-imageRUNNER-6570-Brochure.pdf
https://www.google.com/search?q=canon+ir6570+paper+size
Changing Tray Size Settings
https://www.google.com/search?q=canon+ir6570+change+paper+tray+size
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