what do i use to cut it

thanks so much
It's plastic, so it's more a question of what do you have to cut with?
Xacto/box/utility knife. Pressing firmly, repetitive cuts. Do not try to cut through in one pass. Wood support underneath so you're only applying force to the section you're cutting.
Hack saw. Fine tooth blade
Coping saw. Fine tooth.
Jeweler's saw
Dremel. Fine saw (Gyro's makes a nice set). Cutoff blade, cutting/shaping wheel, Rip & cuttoff blade mounted backwards. I would avoid the other bits. Not that they wouldn't work, but because it's harder to control and keep to the line.
Multifunction tool. Fine toothed blade or the sharp scraper.
Electric carving knife. Don't tell the wife.
Bandsaw. Fine tooth.
Tablesaw. Fine plywood steel blade mounted backwards. This one I would build a jig to keep the saw from catching or pulling the sluice. Actually, I'd use any of the other tools for more control.
Hot wire cutter.
Whatever you end up using, make sure you have a solid work support so you're not applying force to the sluice. IE don't have the sluice upside down and push down hard in the middle.
Layout the cut line with tape - Measure twice, cut once. Leave some tabs or space to attach a flair.