According to the PIC32MX Family Reference Manual - chapter 12 I/O ports (http://ww1.microchip.com/downloads/en/DeviceDoc/61120D.pdf), PIC32s are 5V tolerant when the pins are in INPUT mode. I have read that this may only apply when pins are configured as digital, but unsure about this.
The Microchip Tips'n tricks guide has a chapter on 3.3-5V interfacing here: http://ww1.microchip.com/downloads/en/DeviceDoc/chapter%208.pdf
Sparkfun has an example of a bidirectional interfacing card here: https://learn.sparkfun.com/tutorials/using-the-logic-level-converter
This post indicates that it should be possible to drive a 5V PIC's SPI input using a 3.3V chip without interfacing. Let's see if that is true :-)