How do you chroot into Arch?

To chroot into the system you will first need to Boot Arch Linux from USB or CD. Find the system partitions that you will need to mount. Create a directory to mount the root partition. Mount the root partition.

What bootloader does manjaro use?

In order to boot Manjaro, a Linux-capable boot loader such as GRUB, rEFInd or Syslinux needs to be installed to the Master Boot Record (MBR) or the GUID Partition Table (GPT) of the media containing the Operating System. The boot loader used on official Manjaro installations and generaly suggested is GRUB.