HDG TRACK DEV DURING ARR PROC WHEN AN A320 PIC GETS OFF TRACK DUE TO CONFUSION REGARDING ARR PROCS INTO CYYZ; ON.

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AFTER FLYING FOR OVER 3 HRS; WE REACHED THE CANADIAN AIRSPACE. AS WE GOT CLOSER TO THE ARPT; WE WERE GIVEN MULTIPLE RWY CHANGES THAT MAY HAVE LED TO AN INCORRECT FMS ENTRY. THIS INCORRECT ENTRY CAUSED A MINOR HDG DIFFERENCE BTWN THE FLT PATH AND THE ACTUAL PATH. THE DIFFERENCE WAS DETECTED AND CORRECTED BY ATC WITHIN SECONDS. THE NEW ASSIGNED HDG DID NOT CAUSE OR RESOLVE ANY TFC CONFLICT. WE THEN CONTINUED ON THE APCH AND HAD AN UNEVENTFUL LNDG. FACTORS THAT CONTRIBUTED TO THIS SIT ARE AS FOLLOWS: 1) MULTIPLE RWY CHANGES AT CLOSE PROX TO THE ARPT. 2) CREW UNFAMILIARITY WITH THE ARPT. 3) GLARE FROM SUN MADE SCANNING DIFFICULT. 4) TIME COMPRESSION. 5) LCL PHRASEOLOGY. POSSIBLE SOLUTIONS: 1) RWY CHANGES WITHIN 20 MI OF THE ARPT AND BELOW 10000 FT SHOULD BE PROHIBITED. 2) BETTER GLARE RESISTANT BLINDS AND VISORS. 3) DIFFERENCES IN PROCS AND PHRASEOLOGY SHOULD BE INCLUDED IN THE NOTAM SECTION OF THE RELEASE PAPERWORK. SUPPLEMENTAL INFO FROM ACN 619546: I MAY HAVE INCORRECTLY INTERP THE ARR TO BE YWT.WTRL02 COMMERCIAL PAGE X VERSUS THE YWT.WTRL02 COMMERCIAL PAGE Y AND THE SELECTED FMS ARR WTRL02. AT THE TIME OF THE POSSIBLE PATH ERROR; I MAY HAVE MOMENTARILY PERCEIVED THAT I WAS ON THE INCORRECT ARR AND THEREFORE CORRECTED BY SELECTING HDG MOMENTARILY TO CORRECT PATH TO INOXER VERSUS PENGA WHILE YYZ ATC NOTICED THE HDG AND GAVE A CORRECTIVE VECTOR. THERE WAS NO CONFLICT OF TFC. CONTRIBUTING FACTORS: 1) FMS ARR ACRONYMS D NOT EXACTLY MATCH ARR CHART ACRONYMS. YWT.WTRL02 COMMERCIAL PAGE X VERSUS WTRL02 (FMS). 2) FATIGUE (MULTIPLE TIME ZONES; LCL CIRCADIAN RHYTHM). POSSIBLE SOLUTIONS: 1) REQUIRE FMS AND CHARTS USE THE EXACT SAME ACRONYMS. 2) RWY CHANGES ARE XMITTED VIA ACARS ALONG WITH AN ALERT MESSAGE ALLOWING FOR SOONER RWY IDENT AND MORE TIME FOR A FULL BRIEF. 3) ADOPT EUROPEAN DUTY REGS TO COMBAT FATIGUE. 4) KEEP CREWS FLYING ON INTL DESTS DURING AN ENTIRE MONTH OF FLYING.