You need to check if your highlander has a tow package. If you have the tow package there is no issue with the highlanger. The tow package does not include a hitch. But includes additional transmission cooler, engine oil cooler, higher rpm engine fans, larger radiator and larger alternator. I know in 2016 the highlander did not have the tow package as a option it came on certain models like the LE Plus, XLE and Limited. Check what 2017 models have tow package.
It looks like all models in 2017 have the tow package My search has?? "All 2017 Highlander V6 models come standard with a towing package that allows for a maximum towing capacity of up to 5,000 pounds. The package includes a heavy-duty radiator with engine oil cooler, 200-watt fan coupling, supplemental transmission oil cooler and 150-amp alternator."
We has a 2012 highlander. Very happy with it. Hills and mountains a little slowdown. Soft rear end. we use a 600 lb WDH to compensate. Could get by without it. We are towing a 3023 more heavy and more tongue weight then a 2619.