Probably by virtue of their winning the Championship of the "Canadian National Soccer League" in 1975. Earlier in the 70s the league was dominated by Toronto Croatia, but their strength was probably diluted by then due to involvement in the MSL.
The teams in the league were considered professional and thus did not take part in the Canada National Challenge Cup.
Fron RSSSF website......
1975
GP W L T GF GA Pts
First Division
Toronto Italia 38 25 2 11 98 33 61
First Portuguese 38 26 7 5 79 35 57
Homer 38 24 8 6 95 36 54
Serbian White Eagles 38 23 8 7 105 30 53
Macedonia 38 22 10 6 74 29 50
Hamilton Croatia 38 17 12 9 60 57 43
Hamilton City 38 15 17 6 63 57 36
London City 38 13 16 9 68 72 35
Toronto Croatia 38 11 21 6 40 57 28
Hamilton Italo-Canadians 38 8 27 3 46 109 19
Italia started the competition (against a New York amateur squad, and beat them in a 2 leg match), but then withdrew before they played Leon of Mexico, probably due to lack of travel funds. The eventual winners were Aguila of El Salvador, who beat Leon in a semifinal in which the Leon club left the San Salvador stadium during the second leg because of a fight.
The NASL did not take part, ever, in the competition.
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Copa de Campeones y Subcampeones CONCACAF 1976
Northern Section
Round 1 (Jun 13 & 27)
Toronto Italia Can New York Inter-Giuliana USA 3-2 2-1 5-3x
x CONCACAF list 2nd leg result as 2-1 to NY Inter-Giuliana but do not
mention a penalty shoot-out
Le�n Mex bye
Round 2
Le�n Mex Toronto Italia Can w/o x
x Toronto Italia withdrew
Group 2 (Sep 5 & 19)
Olimpia Hon Real Espa�a Hon 0-0 0-1 0-1x
x results as listed by CONCACAF; however, Olimpia apparently progressed
so the result of the 2nd leg may be reversed
Round 2 (Oct 10)
Diriang�n Nic Olimpia Hon w/o x
�guila ElS bye
x Olimpia withdrew
Round 3 (Nov 2 & 21)
Diriang�n Nic �guila ElS 1-6 1-5 2-11
Caribbean Section
Round 1
(Jun 6 & 18)
Robin Hood Sur Jong Colombia DAn 3-1 1-1 4-2
(Jun 27 & Jul 11)
Christianburg DAn Voorwaarts Sur 1-8 0-12 1-20
(Jul 10 & 16)
Thomas United Guy Palo Seco Tri 0-2 1-4 1-6x
Malvern United Tri bye
x other sources list this club as Trintopec; Palo Seco may be their hometown
Round 2
(Jul 11 & Sep 5)
Robin Hood Sur Malvern United Tri 0-0 2-0 2-0
(Aug 13 & 22)
Palo Seco Tri Voorwaarts Sur 0-4 1-2 1-6x
x other sources list this club as Trintopec; Palo Seco may be their hometown
Round 3 (Oct 17 & 31)
Robin Hood Sur Voorwaarts Sur 3-0 0-0 3-0
Semifinal (Jan 23 & 26, 1977)
�guila ElS Le�n Mex 1-1 abd 3-1x
[?; Walter Mantegazza]
x both legs in San Salvador; Le�n abandoned 2nd leg while leading 2-1
following a fight, and had the match awarded 0-2 against them
Final (Feb 13, 1977)
�guila ElS Robin Hood Sur 5-1 x
x according to the CONCACAF website only one match was played in San Salvador
with as result 5-1; other sources list two matches (with a 6-1 win for
�guila in the 1st leg and a 2-1 win in the 2nd leg); other sources state
Robin Hood forfeited; possibly Robin Hood forfeited after losing the 1st
leg 1-5 or 1-6 and had the 2nd leg awarded 0-2 against them
overview | 1975 | 1977
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The only other Canadian participation...
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Copa de Campeones y Subcampeones CONCACAF 1975
Northern Section
Round 1 (Jul 5 & 13)
Monterrey Mex Toronto Sb. White Eagles Can 2-0 1-1 3-1x
[Alfredo Jim�nez 33, S�nchez 45+]
[?; Rub�n Romeo Corbo]
x 2nd leg abandoned at 1-1 in 67' due to fight; Sb. abbreviates Serbian
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Posted on Feb 1, 2008, 10:23 AM from IP address 190.220.78.203