Do you have any particular laser printers in mind?
Go online and look for the applicable printer User Manual via the manufacturer's website.
Then look for the supported paper sizes and what configuration settings (if any) are needed to use A3/A4 paper.
For example - from my printer's (ink jet) manual.
http://h10032.www1.hp.com/ctg/Manual/c06220009.pdf
Reference physically numbered Pages 45, 46....
Plus you will likely benefit by reading the applicable printer(s) User Manuals in advance of purchasing. Pay attention to the fine print, warnings, caveats, etc..
What you learn may make a difference with respect to the final purchase decision.